Separation is a measure applied to help protect the physical and mental integrity of detainees, to better monitor them individually, and to contribute to their rehabilitation. It also facilitates proper prison management.

International standards clearly stipulate that women should be separated from men, minors from adults, untried persons from convicted detainees, and civil detainees from detainees imprisoned for criminal offenses.

The separation between untried and convicted detainees is based on the principle of the presumption of innocence. It also helps to render effective the different prison regimes that should apply to these two categories of detainees regarding matters such as contact with the outside world, work, or access to vocational training.

The principle of separation can be guaranteed by allocating special facilities for the groups concerned, such as women prisons, or by allocating units strictly separate from each other within the same institution. In the absence of specific institutions due to a shortage of material resources or an insufficient number of inmates concerned to justify their creation, persons in the aforementioned categories should be held in a separate building within the prison grounds or in a strictly separate wing with no possible access to other parts of the institution. In such cases, separation must be guaranteed in regard to cells and dormitories, but also to public areas such as prison shops, exercise yards, and workshops. During movements inside the prison, including in relation to transfers, measures should be taken to avoid contact between the separated categories of detainees. In any case, separation measures should not lead to deterioration in the treatment or material conditions of the persons concerned.

The separation of detainees by category is distinct from their classification. Sentenced detainees should be classified within days of their arrival in prison. This procedure essentially aims to ensure detention conditions that correspond as adequately as possible to their needs, especially from the perspective of personalisation of the sentence’s execution and rehabilitation. Classification is also intended to prevent escape and to minimise the risks of violence and conflict. It is therefore carried out on a case by case basis through the most complete assessment possible of the newly arrived person to determine age, profile, type of crime or offense committed, the level of danger presented by the person to h/herself or others, vulnerability, and special needs, etc. If the classification is different from the separation by category, it may still practice result in a short or long-term separation measure.

The separation of detainees is in no way a disciplinary sanction. As such, it should be clearly distinct from solitary confinement as a disciplinary measure, and should never lead to restrictions of access to services (vocational training, work, etc.).

Certain detainees can be exposed to the risk of violence and abuse by fellow detainees because of their age (young adults or older inmates), health condition, ethnicity, sexual orientation, or gender identity. To minimise these risks and/or eliminate the exposure of these detainees to violence, the authorities must take protective measures that can result in their physical separation, for example by moving them to different cells, units, or even to other institutions in some cases.

These measures should not be systematic or discriminatory vis-à-vis certain groups, and their appropriateness should be periodically assessed. Measures solely intended to protect certain people should always be implemented with their informed consent to avoid arbitrary and/or discriminatory action against them. The detainees concerned are sometimes placed in units for "fragile" or "vulnerable" persons. Such units must ensure for them access to the same care, services and benefits offered to the rest of the detainee population.

In addition, the material conditions of detention should be at least as good as in the rest of the institution. Every effort should be made to ensure that this type of separation does not contribute to stigmatisation of the detainees concerned. Finally, this type of separation should not result in the solitary confinement of detainees in situations of vulnerability.

Detainees living with HIV or AIDS should not be separated from the rest of the prison population solely on the basis of their HIV/AIDS status.

As a matter of principle women should always be separated from men. This measure is primarily intended to protect them from all forms of verbal or physical abuse, particularly sexual violence. Whenever possible, women should be held in separate institutions. In institutions open to both male and female inmates, the premises allocated to women should be entirely separate. In some specific contexts, the authorities may make arrangements to allow couples, where both the male and female partners are deprived of their liberty, to participate together in organised activities. Such activities, designed to improve the quality of life of the people concerned, must ensure the protection of the participants (especially that of the women) and should be adequately supervised.

Minors should be kept separate from adults to prevent potential abuse, including sexual abuse, and harmful influences affecting their development. Exceptions to this rule can only be justified based on the best interest of the child. Separation should also ensure that the detention regime of minors is appropriate to their age, as open as possible, and focused on their rehabilitation. In some cases, under controlled conditions, detained minors may be required to participate with adults in special treatment programmes that have been shown to be beneficial for the juveniles concerned, and if the adults involved have been carefully selected.

Young adults (18-21 years) should also be kept separate from adults and benefit from a special regime appropriate to their age and specific needs.

LGBTI persons are particularly at risk of discrimination and verbal, psychological and physical abuse from other detainees. The separation of an individual or group of LGBTI people can be an effective protective measure in certain situations. However, the identification of LGBTI people should be neither intrusive nor stigmatizing, and their separation from the rest of the prison population should always be decided with their consent. Those who do not wish to reveal their sexual orientation should not be forced to do so. Finally, separation should be an interim measure, and its relevance should be evaluated regularly, and not result in prolonged isolation. LGBTI people who are temporarily separated from the rest of the prison population should retain unrestricted access to the activities, services and benefits available in the institution.

Persons with physical or mental disabilities should not be systematically separated from the rest of the prison population. Some may require specific care or special protection measures, which may necessitate temporary segregation from the rest of the prison population. Such measures should always be implemented with their consent, and with care to avoid stigmatisation. Persons with disabilities who are temporarily separated from the rest of the prison population should retain unrestricted access to activities, services and benefits available in the institution.

Migrants deprived of their liberty for contravening migration laws should not be detained in institutions holding accused or convicted persons. Where applicable, upon their admission migrants should be kept strictly separate from the rest of the prison population, and should benefit from a regime that is as open as possible.

Foreigners and detainees from ethnic and religious minorities or indigenous peoples should have the same rights as the rest of the detained population. They should therefore not be kept separate based solely on ethnic, racial, religious or other such considerations. However, it is possible that some among them are victims of discrimination or violence, particularly of a racist-nature. At their request, and with their consent, they should be able to be temporarily segregated from the prisoners behind the violence. Such separation must not be systematic. In some contexts, the authorities are compelled to segregate detainees according to their origin in order to reduce tension and the risk of conflict and/or violence against minority groups. Such measures should be temporary, non-discriminatory and periodically reviewed, and should never be regarded as an effective long-term measure.